SQL Inner Join Over Multiple Tables Equal to Where Syntax

SQL INNER JOIN over multiple tables equal to WHERE syntax

The query planner takes all WHERE and JOIN predicates into consideration in (almost) the same way, when trying to optimize join order. It's no surprise you get the same performance. Per documentation:

Explicit inner join syntax (INNER JOIN, CROSS JOIN, or unadorned JOIN)
is semantically the same as listing the input relations in FROM, so it
does not constrain the join order.

The only difference: explicit join syntax instructs the given order of joins when the total number of tables is greater than the setting for join_collapse_limit.

And explicit JOINs bind before commas in the FROM list, which is relevant to permissible syntax. Example.

In any case, comma-separated lists of tables in the FROM clause are in no way deprecated. It's just good form and much more readable to use explicit join syntax.

Also note that OUTER joins behave differently in that they cannot be rearranged as freely by the query planner due to logic implications.

SQL Inner join more than two tables

SELECT * 
FROM table1 
INNER JOIN table2
      ON table1.primaryKey=table2.table1Id
INNER JOIN table3
      ON table1.primaryKey=table3.table1Id

INNER JOIN vs multiple table names in FROM

There is no reason to ever use an implicit join (the one with the commas). Yes for inner joins it will return the same results. However, it is subject to inadvertent cross joins especially in complex queries and it is harder for maintenance because the left/right outer join syntax (deprecated in SQL Server, where it doesn't work correctly right now anyway) differs from vendor to vendor. Since you shouldn't mix implicit and explict joins in the same query (you can get wrong results), needing to change something to a left join means rewriting the entire query.

INNER JOIN ON vs WHERE clause

INNER JOIN is ANSI syntax that you should use.

It is generally considered more readable, especially when you join lots of tables.

It can also be easily replaced with an OUTER JOIN whenever a need arises.

The WHERE syntax is more relational model oriented.

A result of two tables JOINed is a cartesian product of the tables to which a filter is applied which selects only those rows with joining columns matching.

It's easier to see this with the WHERE syntax.

As for your example, in MySQL (and in SQL generally) these two queries are synonyms.

Also, note that MySQL also has a STRAIGHT_JOIN clause.

Using this clause, you can control the JOIN order: which table is scanned in the outer loop and which one is in the inner loop.

You cannot control this in MySQL using WHERE syntax.

SQL Inner join 2 tables with multiple column conditions and update

UPDATE
    T1
SET
    T1.Inci = T2.Inci 
FROM
    T1
INNER JOIN
    T2
ON
    T1.Brands = T2.Brands
AND
    T1.Category= T2.Category
AND
    T1.Date = T2.Date

Joining two tables where id does not equal

SELECT * FROM table1
INNER JOIN table2 ON table2.empid = table1.empid AND table2.alt_id <> table1.alt_id

How to join two tables by multiple columns in SQL?

Yes: You can use Inner Join to join on multiple columns.

SELECT E.CaseNum, E.FileNum, E.ActivityNum, E.Grade, V.Score from Evaluation E
INNER JOIN Value V
ON E.CaseNum = V.CaseNum AND
    E.FileNum = V.FileNum AND 
    E.ActivityNum = V.ActivityNum

Create table

CREATE TABLE MyNewTab(CaseNum int, FileNum int,
    ActivityNum int, Grade int, Score varchar(100))

Insert values

INSERT INTO MyNewTab Values(CaseNum, FileNum, ActivityNum, Grade, Score)
SELECT E.CaseNum, E.FileNum, E.ActivityNum, E.Grade, V.Score from Evaluation E
INNER JOIN Value V
ON E.CaseNum = V.CaseNum AND
    E.FileNum = V.FileNum AND 
    E.ActivityNum = V.ActivityNum

How to do an INNER JOIN on multiple columns

You can JOIN with the same table more than once by giving the joined tables an alias, as in the following example:

SELECT 
    airline, flt_no, fairport, tairport, depart, arrive, fare
FROM 
    flights
INNER JOIN 
    airports from_port ON (from_port.code = flights.fairport)
INNER JOIN
    airports to_port ON (to_port.code = flights.tairport)
WHERE 
    from_port.code = '?' OR to_port.code = '?' OR airports.city='?'

Note that the to_port and from_port are aliases for the first and second copies of the airports table.

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